This invention relates to catalysts for the reaction between an isocyanate and an isocyanate-reactive compound and, more specifically, to such catalysts which are latent in character.
Catalysts which promote the reaction between an isocyanate and an isocyanate-reactive compound are known and include, for example, many organometal compounds and amine compounds. Bismuth carboxylate catalysts for the production of urethane elastomers and carpet-backing are described, for example, in U.S. Pat. Nos. 4,742,090, 4,584,362, and 4,611,044. Certain organic zirconium compounds useful as catalysts for the production of urethane compounds are disclosed in U.S. Pat. No. 3,673,159. The use of organic zirconium compounds as viscosity-reducing agents in filled liquid polymers is taught in U.S. Pat. No. 4,423,180.
While bismuth carboxylate catalysts are known, their catalytic effect in promoting the cure of isocyanate-containing compositions is such that the rate of cure is generally linear. While such rates of cure are desirable for some applications, a curing rate wherein there is a slow initial build up of viscosity, but also wherein the reaction mixture completely cures, or cures to a tack-free state within a relatively short period of time is also desirable for many applications. An example of such an application is for the cure of a two part urethane adhesive composition, wherein a "pot life" during which the composition may be handled and/or applied to a substrate before it substantially cures, is desired. Certain mercury compounds are known to be useful as latent catalysts, but their use is not desirable for environmental reasons.